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Câu hỏi: Cho a là số thực dương tùy ý. Mệnh đề nào sau đây đúng?
A. ${{\log }_{3}}\dfrac{3}{{{a}^{2}}}=3-2{{\log }_{3}}a$
B. ${{\log }_{3}}\dfrac{3}{{{a}^{2}}}=1-2{{\log }_{3}}a$
C. ${{\log }_{3}}\dfrac{3}{{{a}^{2}}}=3-\dfrac{1}{2}{{\log }_{3}}a$
D. ${{\log }_{3}}\dfrac{3}{{{a}^{2}}}=1+2{{\log }_{3}}a$
A. ${{\log }_{3}}\dfrac{3}{{{a}^{2}}}=3-2{{\log }_{3}}a$
B. ${{\log }_{3}}\dfrac{3}{{{a}^{2}}}=1-2{{\log }_{3}}a$
C. ${{\log }_{3}}\dfrac{3}{{{a}^{2}}}=3-\dfrac{1}{2}{{\log }_{3}}a$
D. ${{\log }_{3}}\dfrac{3}{{{a}^{2}}}=1+2{{\log }_{3}}a$
Ta có: ${{\log }_{3}}\dfrac{3}{{{a}^{2}}}={{\log }_{3}}3-{{\log }_{3}}{{a}^{2}}=1-2{{\log }_{3}}a$
Đáp án B.